Products known or classified as biodiesel are synthetic liquid fuels obtained from renewable raw materials and made up of mixtures of long chain fatty acid alkyl monoesters derived from vegetable oils or animal fat.
The use of such products as fuel, by themselves or in admixture with other products is well known. The reference international specification for this kind of product is the “Provisional Specification for Biodiesel Fuel (B100) Blend Stock for Distillate Fuels” defined by the American Society for Testing Materials (ASTM) and designed as PS 121-99.
Conventional processes for the industrial production of this kind of fuel are the transesterification unit processes where the triglycerides that make up the vegetable oils or the animal fats are made to react with lower alcohols, in the presence of acidic or basic catalysts.
U.S. Pat. No. 4,695,411 teaches one of these processes for producing a fatty acid monoester composition, useful as a fuel for a diesel engine as a replacement of gas oil. According to the teachings of said US patent, a transesterification of oils or greases of vegetable or animal origin is performed in three distinct steps, using four different anhydrous or hydrated alcohols, in the presence of acidic or basic catalysts.
A similar process is described in U.S. Pat. No. 4,364,743, which provides a list of vegetable oils that was made to react with various alcohols in the presence of the following catalysts: sodium alkoxide, sodium or potassium hydroxide and titanium tetrahydropropoxide (basic catalysts) or the sulfuric, alkyl sulfonic or aryl sulfonic acids.
Other documents forward similar processes with modifications in the production steps of other kinds of biodiesel, none of them mentioning however the straight use of the oleaginous seeds as raw material for the transesterification reaction. These documents are U.S. Pat. No. 5,525,126; U.S. Pat. No. 6,015,440; U.S. Pat. No. 6,174,501 and U.S. Pat. No. 6,211,390.
Other patents, such as for example U.S. Pat. No. 5,578,090; U.S. Pat. No. 6,017,369 and U.S. Pat. No. 6,129,773, teach and prove the technical viability of using several kinds of biodiesel, as such or in admixture with petroleum diesel as a fuel for vehicle or stationary engines.
In one way or another, and at different sophistication levels, the basic feature of these prior art processes is always a transesterification of vegetable oil or animal fat triglycerides, with lower primary alcohols, catalyzed by an acidic or basic, soluble or not, catalyst. Product and by-product (esters and glycerin) refining is performed at different quality and purity grades, after the physical separation of the two liquid phases formed in the reactor after distilling the remaining excess alcohol.
It should be pointed out that in all the cited patents either the process is to be carried out on a high cost, purified or semi-purified vegetable oil, or it is carried out on a sort of waste or by-product having low oil content. This means most of the time a high cost/benefit ratio, since the starting raw material—vegetable oil—has a higher price than the final biodiesel product. Further, according to the state-of-the-art technique, the alcohol, either methyl or ethyl alcohol, even if partly recycled or recovered, must be supplied from external sources. That is why, in spite of the huge government interest of several countries on the biodiesel technology and production, still heavy subsidies are required for supplying biodiesel in gas stations. On the contrary, the process of the present application, by carrying the transesterification reaction on seeds and generating all the required reaction ethyl alcohol, besides other valuable co-products such as pure glycerin, agricultural fertilizers and cattle feed, dispenses with subsidizing and may be produced industrially at a reasonable cost without any burden to the economy.
Brazilian patent PI BR 8003739 teaches a process for extracting vegetable oils from seeds for obtaining a fuel using methyl or ethyl alcohol with the concomitant partial modification of oil into methyl or ethyl esters that are soluble in the corresponding alcohols. The so-obtained fuel is useful for diesel or similar engines. In spite of the reported transesterification reaction and the resulting fuel, the technique of the said Brazilian patent does not lead to a biodiesel product as specified in the above cited ASTM PS 121-99 Method. To begin with, at the time of the research that led to said patent was carried out, the term biodiesel meant the vegetable oil itself, as used in diesel engines. Since petroleum diesel contains C8–C22 hydrocarbon molecules, and vegetable oil C12–C18 moieties linked to a glycerol residue, the similarity of the molecules led to experiments for replacing petroleum-derived molecules for vegetable oils. It should be noted that the heating until the ethyl alcohol boiling point used in the process of PI BR 8003739 entrains vegetable components present in the seeds that are harmful to the produced fuel, such as pigments, vitamins, gum-generating phospholipids and even essential oils. The catalyst used, NaOH, yields soaps that should be withdrawn from the final product. Also, free glycerol is left in the final product, which on burning in the engine yields acrolein, a potent carcinogen. The glycerol amount based on the reaction stoichiometry is nearly 10% by weight of the final product. This is exceedingly more than allowed by the present ASTM PS 121-99, limited to 0.02 wt %.
Therefore, in spite of the state-of-the-art developments, the technique still needs an economically viable process for preparing biodiesel where the transesterification of the triglycerides present in an oleaginous seed be effected directly and integrally on such seeds, dispensing with the step of oil extraction from such seeds and the need to supply ethyl alcohol from external sources while at the same time producing pure glycerin and valuable agricultural co-products, such a process being described and claimed in the present application.